Prestressed joint between bottoms



J. F. HEADRICK PRESTRESSED JOINT BETWEEN BOTTOMS AND SHELLS OF LARGETANKS Filed Sept. 15, 1954 INVENTOR.

JOHN HEADRICK BY A T TORNEVS Aug. 18, 1959 United States Patentpansrnnssnn ronsr BETWEEN BOTTOMS AND,

' snares or LARGE TANKS John F. Hendrick, Berger, Tern, assignor toPhillips Petroleum Company, a corporation of Delaware ApplicationSeptember 13, 1954 Serial No. 455,428

Claims. ((11. 7213).

This invention relates to the construction of large storage tanks and toa prestressed joint between the bottom and the shell of such a tank. Aspecific aspect of the invention pertains to a process or method forprestressing such a joint.

It is conventional to construct concrete bottoms in both old and newsteel storage tanks.

Considerable difficulty with leaks in large steel storage tanks for thestorage of petroleum products, such as oil, and other liquids, has beenexperienced because of the stress applied by the liquid to the shell ofthe tank which separates the shell from the concrete bottom of the tank.Conventional steel tank bottoms corrode inside and outside and musteventually be replaced. Cement or concrete has been used for thispurpose, but the joint between the concrete and the steel shell opens upwhen the tank is filled, thereby permitting corrosive liquids to comeinto contact with the bottom and eventually find its way out of thetank. Conventional concrete water tanks use a sliding joint between thebottom and the shell but these frequently leak also. The leaks causeprogressive damage to the concrete and ultimately the interior of thejoint must be caulked.

The objects of the invention are several and include, to provide animproved tank construction which may be embodied in either a new tank orin an old tank which has a deteriorated bottom; to provide aprestressedjoint between the bottom and shell of a tank; to provide a method ofconstructing such a prestressed joint; and to provide a liquid tightjoint between a tank shell and a cement or concrete bottom which willwithstand liquid pressure without opening up. ()ther objects of theinvention will become apparent from a consideration of the accompanyingdisclosure. I i

In accordance with the invention, a concrete slab or bottom is formed ina tank with a flexible sealing member or means bonded to the verticaledge of the bottom and extending into contact with the shell of the tankalong the upper edge of the sealing member. This sealing means is liquidtight so that when the tank is filled with water or other suitableliquid, the shell of the tank is expanded under the hydraulic pressure,thereby providing an open space between the edge of the slab or sealingmeans bonded thereto and the shell of the tank. While the shell is thusexpanded, a flowable cement, such as grout, is forced into the openspace through openings in the shell adjacent the open space so as tocompletely fill the space. After the cast cement has set and hardened,the shell adjacent the bottom is held in a permanently stressedcondition by the rigid solid annulus of cast cement material so that thetank will hold any storage liquid without expanding in the area of thejoint, thereby avoiding an opening in the joint which will result inleakage and/ or deterioration of the tank.

In a preferred embodiment of the invention, the slab or bottom is formedin the tank to provide .an initial open space intermediate the sealingmeans and the shell "ice of. the tank so as to provide a larger spacefor grout than is provided by expansion alone.

Also, it is preferred that the liquid filling the tank during thegrouting operation have a higher specific grayity than the storedliquid, whereby the initial stress the shell is never entirely removed.7

A more complete understanding of the invention may be had from aconsideration of the accompanying drawing of which Figure 1 is asectional elevation of a preferred embodiment of the invention; Figure 2is a detailed sectional elevation of a bottom corner of a tank showing asrnilar embodiment of the invention; and Figure 3 is a detailedsectional elevation of a bottom corner of a tank having a cement bottomand shell. All of the figures are schematic.

Refe 'lug to Figure 1, a steel tank 10 comprises a steel shell 11 joinedto a steel bottorn 12 by means of steel angle 13, and rivets 14. The,shell and steel bottom may be: fabricated from steel sheet in sectionsby either riveting or welding. The tank has a roof 15 attached to theshell by meansof brackets 16 or other suitable fixtures. A concretebottom or slab 17 covers the bottom of the tank to within a shortdistance of the shell and has bonded -edge a flexible iron or steelsheet 18 so as to provide an open space 19 intermediate sheet 18 andshell 11. Helical concrete, nails, spaced at short intervals around theiperipheryfof the bottom and driven through small holesin flexible sheet18 before pouring of the cement bottorn, serve to hold the sheet inclose bond with the cement after setting. Coarse mesh Wire screen 22 inthe center area of the slab to impart strength to the same. Connectors23 and 24 in openings in the shell provide rneans for forcing grout orother suitable hardening cement into the open space 19 while the shellis expanded by hydraulic pressure.

Referring to Figure 2, corresponding parts of this figure, as well as ofFigure 3, bear numerals corresponding to those, oi Figure 1. It can beseen that the construction in Figure 2 is similar to that of Figure l,the essen tial difference being in the weld 28 utilized to attach theshell 11 to bottom 12. Another diflerence lies in the bottom cutout 29which leaves only an annular section of the steel bottom on which thecement slab is poured. I some p ic t ns the ce te s c n 29 of the tankbott m m be sa ag d o e n m c r as ns- Figure 3 shows new tankconstruction in which .a poured bottom slab '22 having an ofiset section31 as a support or foundation for shell 11 is provided. Wire re afa e nn ar e o t d o th shell i til zed to resist cracking of the shell duringexpansion and to give added strength to the shell. While these heavywires are shown embedded in the concrete, it is also feasible toconstruct the concrete shell in vertical sections and hold the sec tionsin fluid tight relation to each other by means of a .Inultiplicity ofsteel rods or hands around the outside of the shell. Turnbuckles orother tightening means may be utilized to apply tension on the outsideof the shell. The sealing means between bottom 22 and shell 11 in this:type of construction comprises two separate metal sheets 18 and 13a, 18having its upper edge embedded in :lht "Concrete of shell 11 andextending downwardly toward the bottom of the tank and 18a having itslower edge embedded in the tank bottom and extending upwardly along thestep-down edge of the bottom and thence into contact with sheet 18 towhich it is welded by weld 26.

In constructing the perstressed joint of the invention according to themodification shown in Figures 1 and 2, iron .or steel sheet 18 ispositioned in the tank with its upper edge adjacent the shell and itslower edge spaced from the shell by any suitable means, such as bybniallspacers (not shown) which function to hold the sheet in place to resistpressure of the cement while it is fluid. In this manner, with spacersof the desired thickness intermediate shell 11 and flexible sheet 18,the latter is utilized as the form for the edge of the bottom. It isalso feasible to construct removable forms intermediate shell 11 andsheet 18 which can be removed before the upper edge of sheet 18 iswelded to the shell. If spacers are utilized, they should avoid blockingof the flow of grout from section to section of space 19. A suitablearrangement is to place one vertical spacer intermediate each pair ofconnectors 23 and 24 around the base of the shell. It is not necessaryto remove the spacers before filling space 19 with cement.

Elements 21 are firmly fixed in place before the sheet is inserted inthe tank. This can be done by drilling holes smaller than the helicalnails and driving the nails into the holes to bring the heads up solid.Weld 26 may be formed either before or after pouring the bottom but mustbe made prior to filling the tank with water or other liquid. The cementis then poured and allowed to harden and the tank is filled with waterto apply maximum stress on the shell 18 and to elfect as much expansionthereof as will ever occur during utilization of the tank for storage ofliquid. In some instances, it may be desirable to stress the tank with aliquid heavier than water, such as an aqueous solution of solublematerial. When the tank is in this stressed condition and the shell isunder maximum expansion, grout or other suitable hardening cement isforced into space 19 under pressure through connectors 23 until the sameflows out through openings 24 to indicate that the space is filled. Thegrout pressure should not substantially exceed the hydrostatic pressureon sealing means 18 because of the possibility of breaking the sealalong weld 26 and impairing the joint. After the grout is set andproperly hardened, water in the tank can be removed and the tank isready for use in storing any suitable liquid, such as petroleum productsof all types.

Flexible sheet 18 is extended upwardly a small but substantial distanceabove the top surface of the slab or bottom and the space between thissheet and the shell at the edge of the slab is maintained small so as toprovide sufllcient flexibility in the sealing means upon expansion ofthe shell. Other arrangements of the sealing means which permitrelatively small movement of the portion of the sealing meansintermediate the shell and the concrete bottom are feasible and withinthe scope of the invention, in fact, any arrangement which provides aliquid tight seal between the sealing means 18 and both shell 11 andbottom 17 may be used and are within the purview of the invention.

In construction of the tank shown in Figure 3, bottom 22 is poured firstwith sheet 18a and nails 21 fixed in the position shown attached to theforms utilized in forming up the tank bottom. After bottom 17 isproperly set, the forms are removed and forms for shell 11 areconstructed with flexible sheet 18 properly in place inside the forms orextending through a crack in the forms. It is also feasible to attachelement 18 to the concrete by suitable nails and caulking material afterremoval of the forms. The projection of 18a above the bottom may betemporarily bent out of position to allow room for the forms and afterpouring of the concrete of shell 11, 18 may be brought into contact with18a and the weld completed. In instances where shell 11 is constructedof vertical sections, these sections containing element 18 are merelypositioned on the offset portion 31 of slab 17 in proper position andcompression rods or bands traversing the outside of the shell aretightened so as to form a seal between the vertical sections of cement.Caulking material may be used between the joints of the verticalsections to effect a seal. The joints in 18 and the joint with 18a arethen welded so as to form a liquid tight seal between shell 11 andbottom 17. This permits the filling of the tank with a liquid so as toprestress the joint after which grout is forced into the space 19, asdescribed in connection with Figures 1 and 2.

Sealing member 18 is preferably made of relatively thin sheet metal,such as 20-28 gauge black iron. Any other metal may be used which can besuccessfully welded or soldered to provide a liquid tight union betweenthe metal shell and the sheet. It is also feasible to utilize imperviousheavy fabric, such as rubber impregnated woven or cord material, as theflexible sealing member between the bottom of the tank and the shell. Insuch instances, the fabric may be bonded to the cement bottom byextending the lower edge under the cement or into the cement in themanner shown in Figure 3 (element 18 or 18a) and the upper edge of theflexible fabric may be sealed to the shell by means of caulkingcompound. In the conventional large storage tanks, the pressure at thejuncture of the bottom and the shell of the tank is usually in the rangeof 2025 p.s.i.g. It is desirable to prestress the joint to a pressure ofat least 20 p.s.i.g. and preferably to a greater pressure than will everbe exerted by a storage liquid in the tank.

Storage tanks are often found with the peripheral portion in sunkenposition after a long period of service and the method and structure ofthe invention is equally applicable to tanks found in this conditionwithout raising the sunken portion of the tank.

Certain modifications of the invention will become apparent to thoseskilled in the art and the illustrative details disclosed are not to beconstrued as imposing unnecessary limitations on the invention.

I claim:

1. A tank having a generally cylindrical shell and a concrete bottom and-a prestressed sealed joint therebetween comprising an annular flexiblesealing member of flexible sheet material between the side of the bottomand the inside wall of said shell, which sealing member is attachedalong its top to said shell at a short distance above the upper surfaceof said bottom, and a separate cast hardened cement element undercompression completely filling a space formed between said flexiblesealing means and said wall of said shell, which hardened cement elementunder compression is exerting an expanding force on said shell.

2. A tank having a shell and a concrete bottom and a prestressed sealedjoint therebetween comprising a flexible sealing means between the sideof the bottom and the inside wall of said shell and a separate casthardened cement element under compression completely filling a spaceformed between said flexible sealing means and said wall of said shell,which hardened cement element under compression is exerting an expandingforce on said shell, wherein said shell is a steel cylinder and saidflexible sealing means comprises an annular metal sheet attached at itstop edge to said shell at a relatively short distance above the uppersurface of said bottom.

3. A tank having a shell and a concrete bottom and a prestressed sealedjoint therebetween comprising a flexible sealing means between the sideof the bottom and the inside wall of said shell and a separate casthardened cement element under compression completely filling a spaceformed between said flexible sealing means and said wall of said shell,which hardened cement element under compression is exerting an expandingforce on said shell, wherein said shell is a concrete cylinder and saidsealing means comprises a pair of flexible metal sheets, a first sheethaving its upper edge imbedded in said shell and extending downwardlytoward said bottom, a second sheet having its lower edge imbedded insaid bottom and extending upwardly to form a sealed joint with saidfirst sheet.

4. A metal tank ha /ing an upright expansible cylindrical metal wall; arigid concrete bottom within said tank extending to within a shortdistance from said wall forming a narrow annular space between the lowerinside Surface of the tank wall and the outer peripheral wall of thesaid bottom; a separate rigid solid annulus of cast cement materialunder compression in said space and filling said annular space, thusholding said metal wall adjacent said annulus in expanded condition sothat when said tank is filled with liquid said metal wall retains tightcontact with said annulus.

5. The tank of claim 4 wherein said annulus extends above said bottom.

1,138,394 Mueser May 4, 1915 6 Chappell July 3, 1934 McNeil Mar. 31,1936 Walker Jan. 9, 1940 Logeman Nov. 3, 1942 Smith et al. Nov. 9, 1943Pomykala Aug. 14, 1945 Maceratta May 13, 1952 FOREIGN PATENTS France May27, 1953

